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Abstract:

An object is to be capable of inducing a nuclear fusion reaction at a
relatively high efficiency and downsize a device. A nuclear fusion device
1 of the present invention includes a nuclear fusion target 7 including a
target substrate 7a containing deuterium or tritium and a thin-film layer
7b containing deuterium or tritium stacked on the target substrate 7a, a
vacuum container 5 for storing the nuclear fusion target 7, and a laser
unit 3 for irradiating two successive first and second pulsed laser
lights P1, P2 toward the thin-film layer 7b of the nuclear
fusion target 7, and the intensity of the first pulsed laser light
P1 is set to a value that is smaller than that of the second pulsed
laser light P2 and allows peeling of the thin-film layer 7b from the
target substrate 7a.

Claims:

1. A nuclear fusion target for producing a nuclear fusion reaction,
comprising: a first target layer in a flat plate shape having a first
film thickness containing deuterium or tritium; and a second target layer
having a second film thickness thinner than the first film thickness
stacked on the first target layer and containing deuterium or tritium.

2. The nuclear fusion target according to claim 1, wherein the first
target layer is a layer for which hydrogen in a solid material containing
hydrogen has been substituted with deuterium or tritium.

3. The nuclear fusion target according to claim 1, wherein the second
target layer is a metal thin film absorbed with deuterium or tritium.

4. The nuclear fusion target according to claim 1, wherein the second
target layer is a layer for which hydrogen in a solid material containing
hydrogen has been substituted with deuterium or tritium.

5. A nuclear fusion device comprising: the nuclear fusion target
according to claim 1; a vacuum container for storing the nuclear fusion
target; and a laser light irradiating section for irradiating laser light
including two successive first and second pulsed lights toward the second
target layer of the nuclear fusion target, wherein the intensity of the
first pulsed light is set to a value that is smaller than that of the
second pulsed light and allows peeling of the second target layer from
the first target layer.

6. A nuclear fusion method for producing a nuclear fusion reaction
comprising the steps of: disposing in a vacuum a nuclear fusion target
including a first target layer having a first film thickness containing
deuterium or tritium, and a second target layer having a second film
thickness thinner than the first film thickness stacked on the first
target layer and containing deuterium or tritium; and irradiating laser
light including two successive first and second pulsed lights toward the
second target layer of the nuclear fusion target, wherein the intensity
of the first pulsed light is set to a value that is smaller than that of
the second pulsed light and allows peeling of the second target layer
from the first target layer.

Description:

[0002] Conventionally, it has been studied to use laser light in order to
produce nuclear fusion in a highly controlled manner by using a
small-sized and low-cost device. Further, through recent research, a
great improvement in neutron production efficiency by a nuclear fusion
reaction using a laser unit has been expected, and such a neutron
production method using a nuclear fusion reaction has come to be expected
as a safer method than by a nuclear fission reaction.

[0003] As conventional examples of nuclear fusion production methods using
laser light, ones of the following non-patent document 1 and the
following patent document 1 have been known. In the method described in
the following patent document 1, an irradiation member prepared by
coating deuterium substituted plastic on a thin film of Mylar or the like
is momentarily irradiated with laser light to produce high-energy
hydrogen nuclei, and a target member disposed at approximately a
predetermined distance from the irradiation member is irradiated with the
hydrogen nuclei to induce a nuclear fusion reaction. On the other hand,
in the method described in the following non-patent document 1, two laser
pulses are successively made incident at a predetermined time interval
(300 psec) onto a target prepared by forming a film of deuterium
substituted polyethylene (C2D4)X on an aluminum plate to
induce a nuclear fusion reaction.

[0006] However, the nuclear fusion production method described in
non-patent document 1 above, in which the target is plasmatized by the
first laser pulse of the two laser pulses, and then ions in the plasma
are heated to a high temperature by the second laser pulse to induce
thermonuclear fusion, thus requires laser light of a relatively large
energy for making the ion density in the plasma an optimum value to
produce a thermonuclear fusion reaction efficiently. Moreover, in the
nuclear fusion production method described in patent document 1 above,
the energy efficiency is not sufficiently obtained. As a result, there is
a tendency in both methods that it is difficult to produce a nuclear
fusion reaction at a high energy efficiency.

[0007] Therefore, the present invention has been made in view of such
problems, and an object thereof is to provide a nuclear fusion target,
nuclear fusion device, and nuclear fusion method that is capable of
inducing a nuclear fusion reaction at a relatively high efficiency, and
that allows downsizing of the device.

Solution to Problem

[0008] In order to solve the above-described problems, a nuclear fusion
target of the present invention is a nuclear fusion target for producing
a nuclear fusion reaction by irradiating laser light, and includes a
first target layer having a first film thickness containing deuterium or
tritium, and a second target layer having a second film thickness thinner
than the first film thickness stacked on the first target layer and
containing deuterium or tritium.

[0009] Alternatively, a nuclear fusion device of the present invention
includes the nuclear fusion target described above, a vacuum container
for storing the nuclear fusion target, and a laser light irradiating
section for irradiating laser light including two successive first and
second pulsed lights toward the second target layer of the nuclear fusion
target, and the intensity of the first pulsed light is set to a value
that is smaller than that of the second pulsed light and allows peeling
of the second target layer from the first target layer.

[0010] Alternatively, a nuclear fusion method of the present invention is
a nuclear fusion method for producing a nuclear fusion reaction by
irradiating laser light, and includes a step of disposing in a vacuum a
nuclear fusion target including a first target layer having a first film
thickness containing deuterium or tritium, and a second target layer
having a second film thickness thinner than the first film thickness
stacked on the first target layer and containing deuterium or tritium,
and a step of irradiating laser light including two successive first and
second pulsed lights toward the second target layer of the nuclear fusion
target, and the intensity of the first pulsed light is set to a value
that is smaller than that of the second pulsed light and allows peeling
of the second target layer from the first target layer.

[0011] According to such a nuclear fusion target, nuclear fusion device,
or nuclear fusion method, by disposing the nuclear fusion target
including two layers of first and second target layers containing
deuterium or tritium in a vacuum, and irradiating a first pulsed light
toward the second target layer being a thin-film layer, the second target
layer can be peeled from the first target layer. Thereafter, by
irradiating a second pulsed light following the first pulsed light onto
the second target layer with a predetermined time interval, an ion beam
produced from the first target layer can be sufficiently accelerated
toward the second target layer distant at a predetermined distance, so
that a high-energy ion beam can be irradiated onto the first target
layer. As a result, a nuclear fusion reaction can be produced at a high
efficiency in the vicinity of the first target layer, and the production
efficiency of neutrons is also improved. Simultaneously, adopting the
target including the two target layers also makes downsizing of the
device easy.

Advantageous Effects of Invention

[0012] According to the present invention, a nuclear fusion reaction can
be induced at a relatively high efficiency, and the device can be
downsized.

BRIEF DESCRIPTION OF DRAWINGS

[0013] FIG. 1 is a schematic configuration diagram showing a structure of
a nuclear fusion device 1 according to a preferred embodiment of the
present invention.

[0014]FIG. 2 is a conceptual diagram showing an induced state of a
nuclear fusion reaction in the nuclear fusion device of FIG. 1.

DESCRIPTION OF EMBODIMENTS

[0015] Hereinafter, a preferred embodiment of a nuclear fusion device and
nuclear fusion method according to the present invention will be
described in detail with reference to the drawings. In the description of
the drawings, the portions identical to or equivalent to each other are
denoted by the same reference numerals and overlapping description will
be omitted. The drawings are prepared for description, and are drawn so
that the parts to be described are especially emphasized. Therefore, the
dimensional ratios of the members in the drawings are not always
coincident with actual ratios.

[0016] FIG. 1 is a schematic configuration diagram showing a structure of
a nuclear fusion device 1 according to a preferred embodiment of the
present invention. The nuclear fusion device 1 is a device for inducing a
nuclear fusion reaction by laser light irradiation to generate neutrons,
and includes a laser unit (laser light irradiating section) 3 for
irradiating laser light, a vacuum container 5 the interior of which is
maintained in a vacuum state, and a nuclear fusion target 7 stored in the
vacuum container 5.

[0017] The laser unit 3 is a unit capable of irradiating ultrashort pulsed
laser light having a pulse width of approximately 100 fs, using as its
laser medium, for example, titanium-sapphire crystal, and having a
built-in beam splitter section, pulse delay section, beam coupler
section, etc. Moreover, the laser unit 3 is arranged so as to be capable
of successively irradiating ultrashort pulsed laser light at
predetermined time intervals (for example, a few hundred picosecond
intervals). The laser unit 3 is disposed so as to irradiate ultrashort
pulses toward the nuclear fusion target 7 in the vacuum container 5.

[0018] The nuclear fusion target 7 has a double-layer structure including
a target substrate (first target layer) 7a and a thin-film layer (second
target layer) 7b stacked on the target substrate 7a, in which the target
substrate 7a is supported so as to has its surface on the side of the
thin-film layer 7b facing the side of the laser unit 3.

[0019] The target substrate 7a is a solid material in a flat plate shape
having a film thickness of a few hundred micrometers to approximately 1
mm containing deuterium or tritium, and for which hydrogen in the solid
material has been substituted with deuterium or tritium. For example, as
the material of the target substrate 7a, deuterium substituted
polystyrene (C8D8)X for which hydrogen in an organic
material containing carbon and hydrogen such as plastic represented by
polystyrene (C8D8)X has been substituted with deuterium is
used.

[0020] The thin-film layer 7b to be stacked on the target substrate 7a
having the above-described composition is a metal thin film having a film
thickness of 1 μm or less thinner than the target substrate 7a,
containing deuterium or tritium, and prepared by making a metal thin film
absorb deuterium or tritium. For example, as the thin-film layer 7b, a
heavy metal such as titanium or palladium that easily absorbs hydrogen is
used, and the thin-film layer 7b is formed by vapor-depositing such heavy
metal on the target substrate 7a with a film thickness of a few
nanometers to a few tens of nanometers and then making the same absorb
deuterium.

[0021] Here, the target substrate 7a and the thin-film layer 7b may
contain either deuterium or tritium, and may contain both at an
appropriate rate.

[0022] Next, the procedure for inducing a nuclear fusion reaction in the
nuclear fusion device 1 described above will be described in greater
detail, and a nuclear fusion method using laser light according to the
present embodiment will be described.

[0023] First, the nuclear fusion device 1 is prepared, the nuclear fusion
target 7 is disposed in the vacuum container 5 so as to make the
thin-film layer 7b face in a laser irradiating direction of the laser
unit 3, and then the interior of the vacuum container 5 is vacuumed to a
predetermined degree of vacuum.

[0024] Thereafter, a first pulsed laser light having a pulse width of
approximately 100 fs is irradiated from the laser unit 3 onto the
thin-film layer 7b of the nuclear fusion target 7. Further, shortly
thereafter, following the first pulsed laser light with a predetermined
time interval, a second pulsed laser light having a pulse width of
approximately 100 fs to 1 ps is irradiated from the laser unit 3 onto the
thin-film layer 7b of the nuclear fusion target 7. Here, the second
pulsed laser light may include a laser prepulse to generate preplasma.

[0025] At this time, the intensity of the first pulsed laser light is set
to a value on the order of 1015W/cm2 and the intensity of the
second pulsed laser light is set to a value on the order of
1018W/cm2, and the intensity of the first pulsed laser light is
made sufficiently smaller than the intensity of the second pulsed laser
light. The intensity of the first pulsed laser light is set to such an
intensity as to cause peeling of the thin-film layer 7b from the target
substrate 7a and not to plasmatize the material of the thin-film layer
7b. Moreover, the time interval between the first pulsed laser light and
the second pulsed laser light is set to a few hundred picoseconds as such
a value that the thin-film layer 7b is peeled from the target substrate
7a to fly approximately a distance of 1 to 10 μm. Specifically, in the
present specification, "two successive pulsed lights" means two pulsed
lights having such a time interval that the thin-film layer 7b is peeled
from the target substrate 7a to fly approximately a distance of 1 to 10
μm.

[0026]FIG. 2 is a conceptual diagram showing an induced state of a
nuclear fusion reaction in the nuclear fusion device 1. By setting the
intensities and time interval of the first pulsed laser light P1 and
the second pulsed laser light P2 as in the above, the thin-film
layer 7b is peeled from the target substrate 7a shortly after irradiation
with the first pulsed laser light P1, and the second pulsed layer
light P2 is thereafter irradiated onto the thin-film layer 7b at a
timing where the distance D1 between the thin-film layer 7b and the
target substrate 7a has reached approximately 1 to 10 μm. As a result,
in response to the irradiation of the second pulsed laser light P2
onto the thin-film layer 7b, deuterium ions I are generated in the
thin-film layer 7b, and the deuterium ions I are sufficiently accelerated
between the thin-film layer 7b and the target substrate 7a to collide
against the target substrate 7a. In response thereto, a D-D nuclear
fusion reaction is induced between deuterium inside the target substrate
7a and the ions I, and neutrons N generated accordingly are emitted
toward the outside of the vacuum container 5.

[0027] In addition, the irradiation timing of the second pulsed laser
light P2 is preferably a timing where the distance D1 has reached 1
μm or more for sufficient acceleration of deuterium ions, and is
preferably a timing where the distance D1 has reached 10 μm or less so
as not to reduce the density of deuterium ions reaching the target
substrate 7a as a result of diffusion of deuterium ions.

[0028] According to the nuclear fusion device 1 and nuclear fusion method
using the same described in the above, by disposing the nuclear fusion
target 7 including two layers of the target substrate 7a and thin-film
layer 7b containing deuterium or tritium in the vacuum container 5, and
irradiating a first pulsed laser light toward the thin-film layer 7b, the
thin-film layer 7b can be peeled from the target substrate 7a.
Thereafter, by irradiating a second pulsed laser light following the
first pulsed laser light onto the thin-film layer 7b with a predetermined
time interval, an ion beam produced from the thin-film layer 7b can be
sufficiently accelerated toward the target substrate 7a distant at a
predetermined distance, so that a high-energy ion beam can be irradiated
onto the target substrate 7a. As a result, a nuclear fusion reaction can
be produced at a high efficiency inside of the target substrate 7a, and
the production efficiency of neutrons in response to the nuclear fusion
reaction is also improved. Simultaneously, as a result of adopting the
arrangement of the nuclear fusion target 7 consisting of two layers being
disposed in the vacuum container 5, a conventionally used large-scale
accelerator and nuclear reactor are no longer necessary, so that
downsizing of the device also becomes easy.

[0029] In particular, according to the present embodiment, an ion beam
having directionality is made to collide against a target with sufficient
acceleration to induce nuclear fusion, and thus in the case of a low
laser energy condition, more neutrons can be produced relative to the
input energy than by conventional thermonuclear fusion using laser light,
so that a high energy efficiency can be achieved.

[0030] Here, the target substrate 7a is one for which hydrogen in a solid
material containing hydrogen has been substituted with deuterium or
tritium, and thus the disposing structure of the target substrate 7a in
the vacuum container 5 is simplified, and stacking of the thin-film layer
7b onto the target substrate 7a also becomes easy. Further, the thin-film
layer 7b is a metal thin film absorbed with deuterium or tritium, and
thus the stacking process onto the target substrate 7a becomes easy.
Therefore, the manufacturing process of the nuclear fusion target 7 and
the integration process thereof into the nuclear fusion device 1 are in
whole simplified.

[0031] In addition, the present invention is not limited to the foregoing
embodiment. Other materials can also be used as the materials of the
nuclear fusion target 7.

[0032] For example, as the target substrate 7a, a heavy water block for
which heavy water (D2O or T2O) has been frozen and solidified
may be used. In this case, when forming the thin-film layer 7b, the
thin-film layer 7b is formed by vapor deposition in an environment where
the temperature is sufficiently controlled so as not to melt the heavy
water. Moreover, irradiation with laser light for inducing nuclear fusion
is also performed in the same temperature-controlled environment.

[0033] On the other hand, as the thin-film layer 7b, one for which
hydrogen in a solid material has been substituted with deuterium or
tritium, such as deuterium substituted polystyrene (C8D8)X
in a thin film shape, is used, and the target substrate 7a on which the
thin film is stacked may also be used.

[0034] Moreover, as a modification of the present embodiment, an ion
accelerator can also be realized. The ion accelerator is the same in
basic configuration as the nuclear fusion device 1, and is different only
in the component of the target substrate 7a of the nuclear fusion target
7. Specifically, as the material of the target substrate 7a, a film-like
member not containing deuterium or tritium, for example, an organic film
having a film thickness of approximately 10 μm is used, and the
organic film on which the thin-film layer 7b being deuterium absorbed
titanium has been stacked is used as a target. According to such an ion
accelerator, by irradiating the target with double pulsed laser light
containing a first pulsed laser light and a second pulsed laser light,
accelerated ions from the thin-film layer 7b toward the outside can be
produced.

[0035] Here, it is preferable that the first target layer is a layer for
which hydrogen in a solid material containing hydrogen has been
substituted with deuterium or tritium. In this case, the disposing
structure of the first target layer is simplified, and stacking of the
second target layer also becomes easy.

[0036] Moreover, it is also preferable that the second target layer is a
metal thin film absorbed with deuterium or tritium. Adopting such an
arrangement makes the stacking process onto the first target layer easy.

[0037] Further, it is also preferable that the second target layer is a
layer for which hydrogen in a solid material containing hydrogen has been
substituted with deuterium or tritium. Adopting such an arrangement makes
the stacking process of the second target layer onto the first target
layer easy.

INDUSTRIAL APPLICABILITY

[0038] The present invention is used for applications of a nuclear fusion
target, nuclear fusion device, and nuclear fusion method using laser
light, and is capable of inducing a nuclear fusion reaction at a
relatively high efficiency and allows downsizing of the device.